Valorising Slags from Non-ferrous Metallurgy into Hybrid Cementitious Binders: Mix Design and Performance

The environmental impact of ordinary Portland cement (OPC) can be decreased by using alternative precursors, such as non-ferrous metallurgy slags (NFMS), which can be alkali-activated to form an inorganic polymer binder (IP). However, an IP demands the use of a high molarity alkali-solution, which is expensive, has a relative high environmental footprint and limits the use of superplasticizers. In order to tackle these challenges, hybrid binders are proposed, which consist mainly of NFMS, a minor amount of OPC and are activated with a low molarity NaOH solution, in which the superplasticizers can be used effectively. A self-compacting hybrid paste with high early-age strength was developed step-by-step by investigating the effect of different amounts of raw materials on the reactivity, identified by semi-adiabatic calorimetry, and strength development. The obtained optimal hybrid binder formulation was (in wt%) 70 NFMS, 10 ground granulated blast furnace slag, 10 OPC, 8 limestone, 0.9 NaOH, 0.8 plasticizer and 0.3 bassanite; for a water-powder ratio of 0.19, the compressive strength was 20, 41 and 61 MPa at 1, 7 and 28 days, respectively. This study demonstrated that a hybrid binder can be produced from mainly NFMS, which can increase their valorisation potential. Graphical Abstract